1. Field of the Invention
This invention relates to exhaust systems and more particularly relates to measuring air-to-fuel ratios in an exhaust aftertreatment system.
2. Description of the Related Art
Engine performance and exhaust aftertreatment system performance are becoming increasingly important under a growing demand for safe, reliable, and environmentally friendly transportation. One effective and pervasive means for evaluating the performance of these systems is to derive data from engine exhaust. More specifically, an effective means of evaluating the performance of these systems is to measure the oxygen content in exhaust, and derive performance data therefrom, such as the current air-to-fuel ratio.
FIG. 1 is a block diagram of a currently available engine exhaust system 100. The depicted system 100 includes an exhaust stream 110, wide-band oxygen sensor 120, and engine control module (ECM) 130. The wide-band oxygen sensor 120 receives a sample of the exhaust stream 110. The sensor control circuitry, contained in the engine as control module, provides an oxygen pumping current to reach and maintain a stoichiometric balance condition within a reference chamber of the wide-band oxygen sensor (the reference chamber or cell is sometimes referred to as a Nernst cell). The engine control module sources and measures the oxygen pumping current. The measured current is used to calculate the engine's air-to-fuel ratio. Accordingly, the system 100 provides a means of determining an engine's air-to-fuel ratio by measuring the oxygen content of the exhaust.
Though the system 100 enables the engine control module to calculate the air-to-fuel ratio, the system 100 includes several deficiencies. For example, the engine control module may only function with a certain type or model of sensor because each sensor type or model presents the pumping current in a different manner or according to different constraints. Accordingly, substituting the sensor with a different sensor model or type would require the engine control module to be reconfigured according to the new sensor. This can be exceptionally problematic as other engine sensors and systems are likely to depend upon a specific ECM. Further, such a union between the engine control module and the sensor provides a disincentive to switch to less expensive, technically more effective, or otherwise superior sensor.
Additionally, the system 100 only provides for a single sensor, thereby foregoing significant functions. For example, having only one sensor does not enable the system to ascertain the effectiveness of related components such as a catalytic converter. Accordingly, enabling only a single sensor deprives the system of additional functionality.
From the foregoing discussion, it should be apparent that a need exists for a superior apparatus, system, and method that measure a normalized air-to-fuel ratio. Ideally, such an apparatus, system, and method would enable the engine control module to operate with multiple sensors regardless of sensory type, manufacturer, or model.